The following drawbacks have been known with conventional inactivated vaccines and toxoids:
(1) Poor infection prevention in natural infection route: In contrast to a vaccine inoculation route which is subcutaneous, intramuscular, or the like, the natural infection route of bacteria, virus, and the like is the mucosae of nostrils, tracheal tract, intestinal tract, and the like, for example, which is different from the inoculation route. There is a demand for realization of infection prevention via inoculation route adapted to the actual condition of natural infection, particularly of mucosal infection prevention by mucosal vaccination.(2) Low mucosal immunity: In vaccinated subjects, immunoglobulin G (hereinafter abbreviated to IgG or IgG antibody) is mainly produced in the blood to induce humoral immunity. However, since secretory immunoglobulin A (hereinafter abbreviated to IgA or IgA antibody) responsible for mucosal immunity is scarcely produced, it is difficult to expect establishment of mucosal immunity. Necessity and effectiveness of IgA antibody are as follows: IgA antibody is responsible for infection prevention at the mucosae which are portals of droplets and airborne infections into the respiratory organ such as nostrils and tracheal tract as well as oral infection into intestinal tract, i.e. for mucosal immunity, and acts a considerably important role in clinical immunology. Further, in contrast to the IgG antibody that has high specificity to antibody and narrow infection prevention spectrum and is almost ineffective for infection prevention against antigenically varied pathogen, the secretory IgA antibody has cross-immunization property, i.e. cross-neutralization activity; therefore, the secretory IgA antibody has a wider infection prevention spectrum due to the cross-neutralization activity and prevents the infection with variant antigen.(3) Necessity of additional inoculation and mounting cost: Since it is difficult to expect reliable effect only by primary immunization due to low IgG antibody production by one inoculation, it is necessary to increase a blood IgG antibody value by one or more additional inoculations, i.e. by a so-called booster inoculation, based on IgG antibody retention state after the primary immunization. Therefore, expenses and labor are repeatedly required, and, though the effect is observed with elderly, adults, and school children who have opportunities of booster inoculation, the effect is not achieved in some cases with younger children who tend to miss such opportunities, particularly with infants under 2 years old.
To summarize the above-described situation, the conventional inactivated vaccines, toxoids, and the like have the function and effect of enhancing humoral immunity mainly by inducing production of IgG antibody in the blood of vaccinated subjects, and the efficacy thereof has been confirmed. However, since the conventional inactivated vaccines and toxoids have the low IgA antibody production and low mucosal immunity-inducing capacity, they have a limit from the viewpoints of satisfactory function and effect for preventing natural infection. Under the circumstances, many attempts have been made in various aspects for solving the drawbacks of conventional vaccines. For example, there have been qualitative and quantitative improvements of vaccine antigen, experimental production of live vaccine to replace inactivated vaccine, developments of new inoculation route, mucosal vaccine, and the like, screening on adjuvants capable of realizing enhancement of humorous immunization and maintenance of the enhanced humorous immunization, experiments oriented to development of mucosal immunity adjuvant, and the like. However, development of safe and effective mucosal vaccine has not been achieved yet.
Hereinafter, the development of mucosal vaccine will be described.
(1) Increase in amount of vaccine antigen: Attempts have been made for increasing amounts of IgG and IgA antibodies to be secreted to the mucosae by increasing an amount of a vaccine antigen to be subcutaneously or intramuscularly inoculated. For example, attempts have been made for increasing an antibody production amount by adding neuraminidase of a virus membrane protein to a conventional inactivated influenza vaccine, a method of adding MF59 as an adjuvant, and the like. However, such methods have problems such as pain, strong side reaction, and the like.(2) Transnasal administration type inactivated vaccine: For the infection prevention by secretory IgA antibody, which is considered most effective, a method of directly inoculating a liquid split antigen via transnasal inoculation has been tried, but a low IgA production amount is pointed out with the method. Accordingly, in order to raise the IgA antibody producibility, a cholera toxin is added as an adjuvant to the split antigen to raise a mucosal immunological response, i.e. the IgA antibody producibility; however, due to the current situation where safety of the toxin as adjuvant is not ensured, practical utilization thereof has not been realized. Also, a split transnasal inactivated influenza vaccine using an Escherichia coli bacteria heat-liable toxin as an adjuvant [product of Beruna Biotech (Switzerland), trade name: Nasalflu] was admitted in Switzerland as a world's first nasal influenza vaccine and has been marketed from October, 2000. However, since Bell's palsy was detected in 25.2% of the vaccinated subjects in a vaccinated subject group, clinical usage thereof was banned in February, 2004 (Non-Patent Documents 1 and 2).(3) Live vaccine using a cold-acclimated strain capable of intranasal inoculation: a live vaccine [product of MedImmuneV/Accines (USA), trade name: FluMist] for intranasally inoculating a cold-acclimated influenza virus (mixture of 3 strains including two type-A strains and a type-B strain, each of the strains is a reassortant) has been admitted and marketed from June, 2003 in USA (Non-Patent Document 3). An optimum temperature for proliferation of the cold-acclimated strain viruses is 25° C., and the viruses do not proliferate at 37° C. (type-B strain) nor 39° C. (type-A strains). However, since a mechanism of toxin attenuation of the cold-acclimated parent strains has not been clarified, the risk of toxin reversion cannot be denied. Further, though the vaccine is excellent for initialization of immunization due to its capability of penetrating into cells due to its active ingredient which is the live virus, mild influenza symptoms sporadically occur due to the vaccine. Therefore, the vaccine has drawbacks such as unavailability for high-risk human, elderly, and the like who are subject to severe symptoms when infected with influenza, unproven effectiveness against frequent continuous drifts and discontinuous shift of influenza virus antigen, and the like.(4) Other vaccines: Though developments of vector vaccines using a vaccinia virus as a virus vector, attenuated live vaccines employing reverse genetics, DNA vaccines using DNA or cDNA as it is as an active ingredient, and the like have been experimentally conducted, none of them has been put into practical use.
Further, developments of immune adjuvants will hereinafter be described.
(1) Immune adjuvant: An immune adjuvant is a collective term used for substances having modulating activities such as enhancement and suppression of immunological response, and the substances are broadly classified into two categories of those having a dosage form aimed for sustained release, retention, and the like of an antigen in an inoculated subject and those used for enhancement and suppression of immunological response. Among these adjuvants, vaccines and toxoids using aluminum phosphate, alum, and the like have been practically used as the former adjuvant for the dosage form. However, practical utilization of the latter adjuvant for reinforcement and enhancement of immunological response has not been reported. For example, though a bacteria-derived BCG live bacteria, BCG-CWS, endotoxin, glucan and the like, synthetic muramyl dipeptide, levamisole, polyl-polyC, bestatin, and the like, cytokines such as interferon, TNS, and CSF, and the like have been publicly known, it is considered that assurance about safety and effectiveness are required for practical utilization of such adjuvants for the reasons of adjuvant diseases such as arthritis, chronic rheumatoid arthritis, high γ-globulinemia and anemia, insufficient effect, and the like. Also, though a technology (Patent Document 1 and Non-Patent Document 4) of using a pulmonary surfactant protein B derived from higher animal as an adjuvant in order to broadly reinforce induction of humoral immunity has been publicly known, practical utilization thereof has not been reported.(2) Development of adjuvant for mucosal immunity: Though various adjuvants such as pertusis toxin B oligomer (Patent Document 2), cholera toxin (Patent Document 3), Escherichia coli bacteria heat-liable enterotoxin B subunit LTB (Patent Document 4), starch particles (Patent Document 5), cholera toxin B chain protein CTB (Patent Document 6), B subunit of verotoxin 1 (Patent Document 7), oligonucleotide (Patent Document 8), interleukin 12 (Non-Patent Document 7), chitosan (Non-Patent Document 5), and neisserial solubilized surface protein (Non-Patent Document 6) have been developed, none of them has been put into practical use.
As described in the foregoing, the necessity of a switch from the conventional vaccine to be inoculated subcutaneously, intramuscularly, or the like to the mucosal vaccine inducing production of IgA antibody at the mucosae which are the natural virus infection routes is widely and deeply recognized. Particularly, though development and practical utilization of the so-called mucosal vaccine as a new generation vaccine in 21st century for inducing production of IgA antibody and local immunity or mucosal immunity are expected worldwide, such mucosal vaccine has not been achieved. It is considered that the mucosal vaccine has not been achieved since a safe and effective adjuvant for imparting the function of inducing IgA antibody production and local immunity or mucosal immunity has not been specified nor established.    Patent Document 1: JP-T-2002-521460    Patent Document 2: JP-A-3-135923    Patent Document 3: JP-T-10-500102    Patent Document 4: JP-T-2001-523729    Patent Document 5: JP-T-2002-50452    Patent Document 6: JP-A-2003-116385    Patent Document 7: JP-A-2003-50452    Patent Document 8: PCT WO00/20039 pamphlet    Non-Patent Document 1: New Engl. J. Med., Vol. 350, pages 896-903, 2004    Non-Patent Document 2: New Engl. J. Med., Vol. 350, pages 860-861, 2004    Non-Patent Document 3: Cleve. Clin. J. Med., Vol. 70, pages 801-806, 2003    Non-Patent Document 4: Am. J. Respir. Cell Mol. Biol., Vol. 24, 452-458, 2001    Non-Patent Document 5: AdV/Ances Drug Delivery Rev., Vol. 51, pages 81-96, 2001    Non-Patent Document 6: V/Accine, Vol. 21, 3706-3712, 2003    Non-Patent Document 7: Infection and Immunity, Vol. 71, pages 4780-4788, 2003    Non-Patent Document 8: J. neonatal Nursing, Vol. 10, pages 2-11, 2004    Non-Patent Document 9: Biology of the Neonate, Vol. 74 (suppl1), pages 9-14, 1998